Plants experience stress from excessive water loss (water or desiccation stress), and a major factor contributing to the loss of nursery stock is water stress. Some plants, such as the Washington hawthorn, are quite sensitive to water loss. For example, Washington hawthorns that experience water stress for 48 hours have a survival rate of about ten percent, and the plants that do survive have limited root growth. Other plants, such as the Norway Maple, are less sensitive to the effects of water loss, although they also are damaged by excessive water loss. Therefore, limiting the plant damage or plant loss associated with water stress is a significant concern for businesses that require healthy, attractive plants. By preventing water stress throughout post-harvest handling and plant establishment periods, good survival and plant growth can occur.
Antitranspirant coating compositions that reduce water loss from the surface of plants have been described in previous U.S. patents. For instance, U.S. Pat. No. 3,826,671 describes a method for controlling water transpiration from plants using a composition comprising an aqueous emulsion of, by weight, 5-50 percent polyethylene, 2-10 percent of an emulsifier, and a minor portion of wax. U.S. Pat. No. 4,058,409 describes an antitranspirant composition that consists essentially of: (1) an aqueous emulsion of oxidized, emulsifiable polyethylene having molecular weights of about 1000 to about 3400 daltons; and (2) at least 25% polyterpene having molecular weights in the range of about 600 to about 1800 with an acid number of zero. Finally, U.S. Pat. No. 4,943,315 describes an antitranspirant composition that comprises a mixture of an acetylene derivative and a phenylbenzylurea derivative. Antitranspirant compositions, including wax-based compositions, are also commercially available. Many of these antitranspirant compositions include active or inert ingredients in addition to the antitranspirant agent.
Although prior plant coating agents generally reduce a plant's water loss, many permit water loss at a rate detrimental to plants experiencing water stress for extended periods. As a result, prior coating agents have little or no beneficial effect on the survival and growth of desiccation-sensitive plants. Furthermore, procedures for reducing water loss may be effective, but are either difficult to use on a commercial scale or with large plants, such as shrink-wrapping, or inhibit the transmission of essential respiratory or photosynthetic gases. As a result, plants coated with prior coating compositions and experiencing water stress still have low survival rates, extensive dieback (the percent of the plant, measured from the top of the plant to the root, that has dried perceptively) and unsatisfactory new root growth. Therefore, there has long been a need for a plant coating composition that: (1) is easily and uniformly applied to large numbers of plants; (2) reduces water vapor transmission rates; (3) increases plant survival rates and new root growth and decreases dieback following water stress; and (4) is non-phytotoxic.